THE LITERARY 



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OF THE LINNiEAN ASSOCIATION OF PENNSYLVANIA COLLEGE. 



Vol. lir. NOVEMBER, 1846. No. 1. 



PHILOSOPHY OF STORMS. NO. IV. 

 BY PROF. WASHINGTON L. ATLEE, M. D. PHILADELPHIA, PA. 



As I am now approaching that part of the subject whicli requires a 

 frequent nsc of the thermometer, T will give a general idea of its con- 

 struction in ortlcr to make all ac([uainted with this invaluable little in- 

 strument. It consists of a glass tube, not often exceediiig twelve inches 

 in length, of very uniform and small bore, one end of which is blown 

 into a spherical cavity, and the other end hermetically scaled after it has 

 been partly filled with quicksilver, artd all aqueous vapor and air have 

 been expelled by boiling. Heat applied to the spherical cavity, or bulb, 

 now filletl with mercury as just stated, will cause the narrow column of 

 fluid within the tube, or stem, to rise, and cold vvill cause it to fall, and 

 by means of a scale attached, we are enabled to read ofl' the degrees of 

 variation. The scale used in this country is that proposed by Fahren- 

 heit, and is graduated into 180° between two fixed points — called freez- 

 ing and boiling points — obtained Ijy immersing the bulb, in melting ice 

 and in boiling water. The first point-is marked 32°, the other 212°, the 

 graduation being extended both below and above these numbers to a 

 certain extent. Tliis instrument diOers in the object of its construction 

 from the barometer already described — the former determining the tem- 

 perature of bodies, the latter the weight of air. 



The deio-poinl may be ascertained, according to the method first in- 

 troduced by M. Le Roi, by cooling a vessel of thin glass or metal until 

 moisture begins to settle on the outside, and noting tire highest temper- 

 ature at which the deposit takes place. In warm weather cold spring 

 water poured into the vessel will cause the moisture to collect on the 

 outside. In cool weather it will require the addition of ice, or a mix- 

 ture of saltpetre and sal ammoniac ; aiad in very cold weather, to this 

 mixture should be added table suit aird snow or pounded ice. So soon 

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